Increase the size of an encrypted file that is becomming full.
There is no direct way to increase the size of an existing encrypted file. The process involves creating a larger file and copying the old data to the new location:
Close the encrypted file that is becomming full.
Rename the actual file with the suffix OLD to remind you this is the one to be replaced.
Create a new encrypted file with the same name (without the OLD suffix) that is sufficiently larger than the one.
Open (Mount) the encrypted file that is becomming full.
Copy all the files from the full drive to the new larger drive.
Close (Dismount) the old full drive.
When you are sure all the files are in the new drive, delete the old encrypted file.